Add cdssync migration test dataset tooling

Add the cdssync migration test dataset manifest, generator script,
workspace instructions, and gitignore.

This sets the default workflow to:
- generate the dataset locally
- copy it to the test machine with metadata preserved
- verify the copied data before migration testing

cdssync/AGENTS.md

@@ -0,0 +1,53 @@
+# AI Agent Instructions for `cdssync`
+
+These instructions apply anywhere under `/home/aw/code/cds/cdssync`.
+
+## Migration Test Dataset Workflow
+
+For migration test datasets in this workspace, follow this process by default:
+
+1. Generate the dataset locally from this workspace.
+2. Preserve the local generated dataset as the canonical original copy.
+3. Copy the dataset to the test machine using metadata-preserving tooling.
+4. Verify the copied dataset on the test machine before using it for migration testing.
+
+## Generation Rules
+
+- Use `/home/aw/code/cds/cdssync/generate_migration_test_dataset.sh` to create the dataset unless the user explicitly asks for a different method.
+- Prefer `/home/aw/code/cds/cdssync/migration-test-dataset` as the local canonical dataset location unless the user specifies another target.
+- If ACL/xattr coverage matters, ensure the generation host has:
+  - `acl` installed for `setfacl` and `getfacl`
+  - `attr` installed for `setfattr` and `getfattr`
+
+## Copy Rules
+
+- Use `rsync -aHAX` by default when copying the dataset to another machine.
+- Preserve permissions, timestamps, symlinks, hard links, ACLs, and xattrs.
+- Do not use GUI copy/paste or non-preserving copy methods for this dataset unless the user explicitly asks for that.
+
+## Verification Rules
+
+After copying to a test machine, verify at least:
+
+- file and directory structure
+- permissions
+- symlinks
+- hard links
+- timestamps
+- ACLs
+- xattrs
+
+Preferred verification commands include:
+
+- `find DEST_DIR | sort`
+- `stat DEST_DIR/regular/script_3mb_700.sh`
+- `stat DEST_DIR/readonly-dir/locked_text_1mb_444.txt`
+- `readlink DEST_DIR/links/symlink_to_text_1mb_644.txt`
+- `stat DEST_DIR/regular/random_3mb_644.bin DEST_DIR/links/hardlink_to_random_3mb_644.bin`
+- `getfacl -p DEST_DIR/metadata/acl_text_1mb_644.txt`
+- `getfattr -d DEST_DIR/metadata/xattr_text_1mb_644.txt`
+
+## Destination Host Requirements
+
+- If the destination host lacks `acl` or `attr`, ACL/xattr verification will be incomplete.
+- If the destination filesystem does not support ACLs or xattrs, those attributes may not survive transfer even when the copy method is correct.